Which of the following statements are correct?
A. The process of generation of conduction electrons and holes and process of recombination is a simultaneous process.
B. To increase the conductivity of a semiconductor manifold, a few parts per million of a suitable impurity is added.
C. Extrinsic semiconductors doped with trivalent impurity are called n-type semiconductors.
D. During the formation of a p-n junction, two processes diffusion and drift occurs.
E. The thickness of depletion region is of the order of a millimeter.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B and D Only
A. The process of generation of conduction electrons and holes and process of recombination is a simultaneous process. — Correct. In a semiconductor, electron-hole pairs are generated by thermal energy and recombine at the same time; at equilibrium the two rates are equal.
B. To increase the conductivity of a semiconductor manifold, a few parts per million of a suitable impurity is added. — Correct. Doping with a few ppm of a suitable impurity raises the conductivity many times.
C. Extrinsic semiconductors doped with trivalent impurity are called n-type semiconductors. — Incorrect. A trivalent impurity (such as boron) has one electron too few to complete the bonds and creates a hole; it gives a p-type semiconductor. An n-type semiconductor is doped with a pentavalent impurity.
D. During the formation of a p-n junction, two processes diffusion and drift occurs. — Correct. Carriers diffuse across the junction; the field of the ions left behind causes an opposite drift, and equilibrium comes when the two are equal.
E. The thickness of depletion region is of the order of a millimeter. — Incorrect. The depletion region is very thin, about one-tenth of a micrometre (\( 10^{-7}\,\mathrm{m} \)), not a millimetre.
NCERT (2026-27):
Intrinsic Semiconductor – “… It may be noted that apart from the process of generation of conduction electrons and holes, a simultaneous process of recombination occurs in which the electrons recombine with the holes.”
Extrinsic Semiconductor – “… When a small amount, say, a few parts per million (ppm), of a suitable impurity is added to the pure semiconductor, the conductivity of the semiconductor is increased manifold.”
p-n Junction Formation – “… Two important processes occur during the formation of a p-n junction: diffusion and drift.”